Method for passing optical fibers through tubular products by vibrating the tubular products

ABSTRACT

A tube is wound into a coil, and the resulting coil of tube is vibrated so that a given point of the tube reciprocates along a helical path. An optical fiber is fed into the coil of tube that is being thus vibrated. Because of the vibration, the inner wall of the tube exerts such a force as to move the optical fiber diagonally upward and forward. This force causes the optical fiber to jump in the tube diagonally upward and forward and slide forward along the inner wall of the tube. The intermittent conveying force exerted by the inner wall of the tube in the direction of the circumference of the coil causes the optical fiber in the tube to travel forward, thereby pulling in additional length of the optical fiber from outside the tube.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method and apparatus for passing opticalfibers through tubular products, and more particularly to a method andapparatus for making optical fiber core wires, optical fiber cordsand/or optical fiber cables comprising optical fibers passed throughprotective tubes or sheaths.

For the purpose of this invention, optical fibers are defined as elementfibers comprising a core and a cladding layer, such element fibers asare coated with syntetic resins, metals and ceramics and theirvariations comprising a single fiber, multiple fibers and strandedfibers. Tubular products are such metal tubes as those of steel andaluminum, and such nonmetal tubes as those of plastic.

2. Description of the Prior Art

Recently optical fiber cables have come to be used widely forcommunications services. And many of them are metal-coated to make upfor limited strength of optical fibers.

Optical fibers passed through metal and other tubes have been made by amethod that combines tape forming and welding (such as that disclosed inJapanese Provisional Patent Publication No. 46869 of 1985) and a methodthat passes an optical fiber through a tube (such as that disclosed inJapanese Provisional Patent Publication No. 25606 of 1983).

In the former method, an optical fiber is passed through a metal tubewhile a metal tape is being formed into a tubular shape and both edgesof the tape are being welded together. But there is a shortcoming thatthe optical fiber is liable to degenerate under the influence of weldingheat when it passes the welding point. Also, an optical fiber isdifficult to pass through tubes whose diameter is as small as 2 mm orunder.

In the latter method, an aluminum tube is made with a steel wire passedtherethrough. After the tube is subjected to a diameter-reducingprocess, the steel wire inside the tube is replaced with an opticalfiber. This method requires intricate processes. Besides, the force withwhich the steel wire is pulled out for replacement should not exceed thestrength of the optical fiber in order to avoid the risk of fiberbreaking. Accordingly, optical fiber cable having a length of 200 m ormore have been difficult to make.

SUMMARY OF THE INVENTION

In an optical fiber passing method of this invention, a tube is shapedinto a coil form, and the coil of tube is vibrated so that a given pointof the tube reciprocates along a helical path. An optical fiber is fedinto the tube from one end thereof while the coil of tube is thus beingvibrated. Consequently, the optical fiber in the tube moves forwardalong the circumference of the coil of tube because of the conveyingforce intermittently exerted by the inner wall of the tube.

To facilitate passing, the difference between the inside diameter of thetube and the diameter of the optical fiber should be not less than 0.1mm and the diameter of the coil of tube should be not smaller than 150mm or preferably 300 mm or more. For the matter of vibration, the angleof vibration (i.e., the lead angle of helix) should be not smaller than1 degree, or preferably between 5 and 30 degrees, the frequency ofvibration not less than 5 Hz, or preferably between 10 and 30 Hz, andthe total amplitude of vibration in terms of vertical component not lessthan 0.1 mm, or preferably between 0.5 and 2.0 mm.

An apparatus for passing an optical fiber through a tube according tothis invention comprises a cylindrical member consisting of a coil ofthe tube through which the optical fiber is to be passed, a device tovibrate the cylindrical member so that a given point of the tubereciprocates along a helical path, and a device to feed the opticalfiber into the coil of tube being vibrated from one end thereof. Thepassing apparatus may also incorporate a sensor to detect the differencebetween the passing speed and feed speed of the optical fiber and adevice to control the feed speed of the optical fiber feeding device onthe basis of the speed difference detected by the aforementioned sensor.

The method and apparatus of this invention permits passing an opticalfiber through a tube of small diameter (such as one having an outsidediameter of 2 mm or under) and long length (such as one having a lengthof 1 km or over) without deteriorating or damaging the optical fiber.Their simplicity is conducive to cutting down the production cost ofoptical fibers covered with protective tubes. With the feed speed of anoptical fiber controlled by the feed device of this passing apparatus,the optical fiber can be fed into a tube in the most favorablecondition, without applying excessive tension on the optical fiber andexerting any backward force to prevent the admission thereof into thetube.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation showing a preferred embodiment of an opticalfiber passing apparatus according to this invention;

FIG. 2 is a plan view of a vibrating table of the same apparatus;

FIG. 3 is a front view showing an example of a bobbin mounted on thevibrating table;

FIGS. 4a and 4b show cross-sectional profiles of grooves cut in thebobbin;

FIG. 5 is a cross-sectional view of an example of an anti-vibratingguide provided in the apparatus;

FIG. 6 is a cross-sectional view of an example of a protective guideprovided in the apparatus;

FIG. 7 illustrates a principle on which an optical fiber is carriedforward in a tube;

FIGS. 8a and 8b diagrammatically show vibrating conditions of a coil oftube;

FIGS. 9a and 9b show front views of other examples of bobbins;

FIG. 10 is a front view showing an example of means to fasten a coil oftube to a bobbin;

FIG. 11 is a perspective view showing an example of an elastic belt usedas the fastening means;

FIG. 12 is a front view showing another example of the means to fasten acoil of tube;

FIG. 13 is a perspective view of a bobbin used with the fastening meansshown in FIG. 12;

FIG. 14 is a front view of an elastic belt used with the fastening meansshown in FIG. 12;

FIG. 15 is a partially cross-sectional front view showing still anotherexample of the means to fasten a coil of tube;

FIG. 16 is a cross-sectional view showing another example of theanti-vibrating guide; and

FIG. 17 is a cross-sectional view showing another example of theprotective guide provided at the inlet end of a tube.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now preferred embodiments of this invention will be described byreference to the accompanying drawings. FIG. 1 is an overall view of apassing apparatus according to this invention, and FIG. 2 is a plan viewof a vibrating table.

A base 11 is firmly fastened to a floor surface 9 so as not to vibrate.Coil springs 18 to support a vibrating table are mounted at the fourcorners of the top surface of the base 11.

A square panel-like vibrating table 14 is placed on the base 11, withthe support springs 18 interposed therebetween. A support frame 15extends downward from the bottom surface of the vibrating table 14.

The support frame 15 under the vibrating table 14 carries a pair ofvibrating motors 21, 22. The vibrating motor 22 is placed diametricallyopposite motor 21 relative to central axis C of table 14. The rotatingshafts of the vibrating motors 21, 22 are respectively parallel to avertical plane containing the central axis C and oppositely tilted withrespect to the surface of the vibrating table at an angle of 75 degrees.Unbalanced weights 24 are fastened to both ends of the rotating shaftsof the vibrating motors 21, 22. The centrifugal force resulting from therotation of the unbalanced weights 24 applies a vibrating force to thevibrating table 14 that works aslant to the surface thereof. The pairedvibrating motors 21, 22 are driven in such a manner that vibrations theycause have equal frequency and amplitude, and vibrating forces theyexert are displaced 180 degress from each other. Accordingly, when thevibrations caused by the paired vibrating motors 21, 22 are combined,the vibrating table 14 vibrates in such a manner so as to move along ahelical path whose central axis coincides with the central axis C of thevibrating table 14. The vibration of the vibrating table 14 is nottransmitted to the base 11 because the support spring 18 are interposedtherebetween.

In place of the vibrating motors 21, 22, such vibrating means as thoseemploying cranks, cams or electromagnets may be used. Also, vibratingmotors 21, 22 may be fastened to the vibrating table 14 in other waysthan shown in FIG. 1.

A bobbin 27 is fastened on the vibrating table 14 in such a manner thatthe axis of the bobbin 27 coincides with the central axis C of thevibrating table 14. A tube 1 through which an optical fiber 7 is to bepassed is coiled around the bobbin 27, forming a coil of tube 5. Theoptical fiber 7 is fed into the tube 1 from the lower end of the coil oftube 5. To avoid the development of excessive bending stress in theoptical fiber, the diameter of the coil of tube should preferably be notsmaller than 150 mm. The optical fiber 7 used in this embodimentconsists of an element optical fiber precoated with resin. The tube 1 isa steel tube. The outer periphery of the bottom flange 29 of the bobbin27 is fastened to the vibrating table 14 with fastening jigs 31 so thatthe vibration of the vibrating motors 21, 22 is surely received. As isshown in FIG. 3, a groove 30 is cut around the circumference of thebarrel 28 of the bobbin 27 using a shaper so that ridges and recessespointing to the axis of the bobbin are successively formed. The groove30 is shaped so that the tube 1 comes in contact therewith closely. Incross-sectional profile, the groove 30 may be either a triangular groove30a as shown at (a) of FIG. 4 or an arc-shaped groove 30b as shown at(b) of the same figure. Any other cross-sectional profile is allowableso long as the tube 1, which is shown by a broken line, is firmlyretained on the bobbin 27.

The optical fiber 7 is passed through gradually while the bobbin 27 isbeing vibrated. If the directly vibrated bobbin 27 and the tube 1 woundtherearound are not kept in close contact with each other, precisetransmission of the vibration to the tube 1 and, therefore, smoothpassing of the optical fiber 7 will not be achieved. The tube 1 woundaround the barrel 28 of the bobbin 27 easily clings to the barrel 28 inthe direction of the diameter of the bobbin 27, but not in the directionof the axis thereof. Then, it becomes difficult to uniformly vibrate theentirety of the tube 1 vertically. But if the tube 1 is held tightly inthe groove 30 around the barrel of the bobbin 27, the vibration of thebobbin 27 will be precisely transmitted to the tube 1, thereby ensuringsmooth and efficient vibration and passing of the optical fiber 7.

A feed spool 37 that constitutes an optical fiber feeder 33 is placedbeside the bobbin 27. The feed spool 34 is rotatably supported on abearing stand 35. The feed spool 34 pays off the optical fiber 7 woundtherearound into the coil of tube 1. The point at which the feed spool34 pays off the optical fiber 7 is substantially at the same level asthe point at which the optical fiber 7 is fed into the tube 1.

A drive motor 38 is positioned next to the feed spool 34. The feed spool34 and drive motor 38 are connected by a belt transmission 40. Rotatedby the drive motor 38, the feed spool 34 pays off the optical fiber 7into the tube 1 wound around the bobbin 27.

A support guide 43 is provided near the optical fiber pay-off point ofthe feed spool 34. Consisting of a short tubular guide proper 44 and astand 45 that horizontally supports the guide proper, the support guide43 supports the optical fiber 7 paid off from the feed spool 34.

An optical fiber feed condition sensor 47 is installed downstream of thesupport guide 43. The optical fiber feed condition sensor 47 is made upof a support column 48 and an optical fiber level sensor 49 attachedthereto. The optical fiber level sensor 49 consists of an image sensorand an oppositely disposed light source. Installed in the pass line ofthe optical fiber 7, the optical fiber level sensor 49 senses thesagging condition thereof. A CCD line sensor is used as the imagesensor.

To the optical fiber feed condition sensor 47 is connected a rotationspeed controller 52 that controls the voltage of power supply 39 to saiddrive motor 38 on the basis of signals sent from the optical fiber feedcondition sensor 47. That is, the rotation speed of the drive motor 38or, in other words, the pay-off speed of the optical fiber 7 iscontrolled depending on the level at which the optical fiber 7interferes with the travel of light from the light source in the opticalfiber level sensor 49.

The speed with which the optical fiber 7 is passed through the tube 1 isnot always constant but may vary when a resonance occurs or depending onthe condition of the inner surface of the tube 1 and the surface of theoptical fiber 7. A change in the running speed of the optical fiber 7 inthe tube 1 affects the feeding condition of the optical fiber 7 on theoutside. If the feed speed does not follow the passing speed, theoptical fiber 7 may either sags excessively or break as a result ofovertight stretching. Either way, smooth feeding of the optical fiber 7will be hindered. But the optical fiber 7 can always be fed at a feedspeed within the desired range if the feed spool 34 is rotated so thatthe rotation thereof is varied or stopped depending on the travellingcondition of the optical fiber 7 in the tube 1. Namely, the opticalfiber 7 is then kept in the optimum condition (in which the opticalfiber 7 sags slightly as shown in FIG. 1), without oversagging orgetting overstretched. As a consequence, the optical fiber 7 is passedthrough the tube without a hitch, with no load placed thereon or noresistance built up against the passing thereof. Incidentally, anoptical fiber 0.4 mm in diameter will not enter a steel tube having aninside diameter of 0.5 mm if a force of 20 gf or greater directed to thefeeder side works on the optical fiber.

The optical fiber feed condition sensor 47 is not limited to theillustrated image sensor, but may consist of a pair of photoelectrictubes that are vertically spaced to detect the upper and lower limits ofthe sagging of the optical fiber 7. In this case, the drive motor 38 ison-off controlled. Instead of sensing the position and form of theoptical fiber 7, just the feed speed of the optical fiber 7 may besensed to control the motor speed in accordance with signals based onthe sensed results.

An anti-vibrating guide 54 is installed between the optical fiber feedcondition sensor 47 and the inlet end 2 of the tube. The anti-vibratingguide 54 consists of a cylindrical guide proper 55 and a stand 58 thathorizontally supports the guide proper. As shown in FIG. 5, both ends ofthe guide proper 55 of the anti-vibrating guide 54 expand outward toform tapered (funnel-shaped) portions 57. The boundary between eachtapered portion 57 and a cylindrical portion 56 should preferably beshaped into a smooth curved surface. The length of the anti-vibratingguide 54 may be chosen appropriately depending on the distance betweenthe inlet end 2 of the tube and the feed spool 34. When the distance islong, the anti-vibrating guide 54 should naturally be long. Theanti-vibrating guide 54 must be made of such materials as glass andplastic that have such a low coefficient of friction that the transferof the optical fiber by vibration is not impeded.

A lubricant feeder 59 filled with a lubricant is attached to thecylindrical portion 56 of the anti-vibrating guide 54. The lubricant isa solid lubricant comprising a powder of carbon, talc, molybdenumdisulfide and so on. The lubricant S that falls from the lubricantfeeder 59 into the cylindrical portion 56 adheres to the surface of theoptical fiber when passing therethrough.

When the coil of tube 5 into which the optical fiber 7 has been insertedis vibrated, the optical fiber 7 immediately ahead of the tube 1 mayswing wildly. The swinging optical fiber 7 may impede smooth vibrationand passing thereof and, at the same time, may damage the surfacethereof on coming in contact with the edge of the inlet end 2 of thetube 2. When the swing is very wild, even cracks may occur inside theoptical fiber. But the anti-vibrating guide 54 keeps down the swingoutside the end of the tube 1, thereby allowing the optical fiber 7 tobe conveyed in good condition, without damaging the optical fiber 7 andoffering no resistance to the vibration and passing thereof.

A separately prepared protective guide 61 is fastened to the inlet endof the tube 1, as shown in FIG. 6. The protective guide 61 is made ofsuch material as plastic that has a low coefficient of friction andprovided with a tapered guide 62 having an outwardly diverged surface.

The optical fiber 7 passed through the coiled tube 1 by the vibration ofthe tube 1 may move forward while bumping against the inlet end 2 of thetube 2 because the optical fiber 7 is also vibrating. Then, the edge ofthe inlet end 2 of the tube may produce longitudinal scratches on theoptical fiber 7 which may cause the cracking of the optical fiber 7 andthe deterioration of a final product. But the protective guide 61 of theabove-described structure enables the optical fiber 7 to be readilyinserted into the tube 1 and smoothly carried forward therein, withoutcausing any surface defect or damage after insertion.

Next, a method of passing an optical fiber 7 through a tube 1 using theabove-described apparatus will be described.

In advance, a coil 5 is formed by winding a tube 1 around a bobbin 27,while an optical fiber 7, which consists of a precoated element fiber,is wound around the feed spool 34. The tube 1 need not always be woundaround the bobbin 27 in a single ring, but can be wound in multiplerings. In a coil of multiple rings, the first ring fits closely in agroove 30 cut around the barrel 28 of the bobbin 27, but the second andsubsequent rings will fit in the recessed portion formed between turnsof the tube 1 of the preceding ring. Then, the bobbin 27 carrying thewound tube 1 is fastened on the vibrating table 14 in such a manner thatthe axis of the coil coincides with the central axis C of the vibratingtable 14. The leading end of the optical fiber 7 pulled out of the feedspool 34 is inserted through the protective guide 61 into the inlet endof the tube, after passing through the support guide 43, optical fiberfeed condition sensor 47 and anti-vibrating guide 54. With the inlet end2 of the tube being positioned at the lowermost end of the the coil 5,the optical fiber 7 is passed through the tube 1 substantially along thetangent of the coil or tube 5.

In the beginning, a length of the optical fiber 7 of 5 to 150 m ismanually pushed into the coil of tube. After this, the inner surface ofthe vibrating tube exerts adequate conveying force to cause the opticalfiber to steadily move forward through the tube. The length of thepushed-in optical fiber (i.e., the length of initial insertion) dependson the inside diameter of the tube, outside diameter of the opticalfiber, and coefficient of friction between the optical fiber and theinner wall surface of the tube. The insertion is readily achieved if theoptical fiber is inserted while vibrating the tube. To ensure the smoothentry of the optical fiber into the tube, a certain amount of clearancemust be left between the optical fiber and tube. The clearance shouldpreferably be not less than 0.1 mm.

When the vibrating motors 21, 22 are started, the vibrating table 14 issubjected to a torque working around the central axis C thereof and aforce working therealong because of the position and posture in whichthe vibrating motors 21, 22 are placed as described previously.Consequently, a given point on the vibrating motors 21, 22 vibrates insuch a manner as to move along a helical H shown in FIG. 1. Thevibration is transmitted from the vibrating table 14 through thefastening jigs 31, bobbin 27 and coil of tube 5 to the optical fiber 7.

The motion of the optical fiber varies with the type of the vibration,properties of the optical fiber, inside diameter of the tube and otherparameters. The optical fiber is considered to move forward through thetube in the following manner.

As is shown in FIG. 7, the bottom surface of the inner wall of the tubeis moving with a vibration V centered on 0. While the angle of thevibration is θ, the maximum acceleration is n times (n sin θ>1) theacceleration g of gravity. The optical fiber is assumed to contact thebottom surface of the inner wall at pitches L since it is hardlyconceivable that the optical fiber is in contact therewith throughout. Apoint of contact is defined as a. The optical fiber is released when thevertical downward acceleration of the bottom surface of the inner wallbecomes equal to g, namely at a point of release P₁ on a line of releasel₁. The release optical fiber begins to jump at a speed v₁ and an angleof projection θ. Meanwhile, a non-contact point b moves differently fromthe point of contact a since the optical fiber is not a rigid substance.The vibration V does not produce as much lifting force as at the pointof contact a. After being released on the line of release l₁, therefore,the optical fiber is subjected to a depressing force resulting from themotion of the point of contact a. Consequently, the optical fiber fallsonto a line of contact l₂ at another point of contact b₁ that isdifferent from the first point of contact a. If the vibration V of thebottom surface of the inner wall is in the rising direction, the opticalfiber continues to move upward until it is released on the line ofrelease l₁. If the vibration V is in the descending direction, theoptical fiber first drops to the lowermost point and then moves upwarduntil it is similarly released on the line of release l₁. Such a surgingmotion is repeated in each cycle or several cycles of the vibration,whereby the optical fiber is caused to move forward through the tube.The most efficient way is such that the optical fiber begins to jumpupward the moment it touches the bottom surface of the inner wall whenthe line of contact l₁ agrees with the line of release l₂.

Strictly speaking, friction, repulsion and other phenomena occuringbetween the optical fiber and the bottom surface of the inner wall ofthe tube must be considered. If the jumping optical fiber comes incontact with the top surface of the inner wall of the tube, theadvancing motion thereof will naturally be different.

When n sin θ≦1, the optical fiber will not jump, but may slide forwarddepending on the condition of friction between the optical fiber and thebottom surface of the inner wall of the tube.

As is obvious from the above, the optical fiber 7 is driven forwardthrough the tube 1 by a component of a force exerted by the inner wallof the tube 1 in the circumferential direction of the coil of tube.Because the axis of the coil of tube is in agreement with the centralaxis C of the vibrating table 14, the optical fiber 7 in the tube makesa circular motion about the central axis C (a circular motion in thecounterclockwise direction P in the embodiment shown in FIG. 2).

Reference is now made to FIG. 1 again.

When the helical vibration is transmitted through the vibrating table 14to the coil of tube 5, the optical fiber 7 fed from the inlet end 2 ofthe tube below the coil of tube 5 continuously moves forward through thetube 1 under the influence of the conveying force resulting from thevibration. That is, the vibration of the coil of tube 5 moves theoptical fiber 7 paid off from the feed spool 34 forward through thesupport guide 43, optical fiber feed condition sensor 47, anti-vibratingguide 54, protective guide 61, inlet end 2 of the tube, coil-formed tube1 and outlet end 3 of the tube. Thus, the optical fiber 7 is passedthrough the entire length of the coil of tube 5 in a given time.

Any variation in the passing speed of the optical fiber 7 affects thefeed condition thereof at the optical fiber level sensor 49, with theresulting change in the feed condition being instantly detected by theoptical fiber level sensor 49. If the optical fiber level sensor 49senses that the optical fiber 7 is overstretched, a corresponding signalwill be sent to the drive motor 38 to increase the rotation speed of thefeed spool 34, thereby increasing the feed speed of the optical fiber 7.If the excessive sagging of the optical fiber 7 is sensed, the drivemotor 38 will be accordingly controlled to slow down the feed speed ofthe optical fiber 7. In this way, any abnormal condition in the forwardtravel of the optical fiber is instantly sensed, corrected and returnedto the normal condition.

(Example)

To confirm the effect of this invention, optical fibers were passedthrough steel tubes under the following conditions (Table 1) using theapparatus shown in FIG. 1. The result of passing are shown in Table 1.

(1) Specimens

Coils of steel tubes:

Seven types of steel tube coils prepared by winding seven differentsteel tubes ranging between 0.8 mm and 2.0 mm in outside diameter andbetween 0.5 mm and 1.6 mm in inside diameter and having a length of 10km regularly (in 10 to 20 rings) around steel bobbins having a barreldiameter of 1200 mm.

Optical fibers:

Optical fibers, 0.4 mm in diameter, of silica glass (125 μm in diameter)coated with silicone resin.

(2) Vibrating conditions:

Because the numbers of rings were 10 (Coils Nos. 1 to 6 in Table 1) and20 (Coil No. 7) on the steel tube coils tested, vibrating conditionswere substantially the same at any point of the tube.

Angle of vibration with respect to the horizontal plane of the coil: 15degrees

Frequency of vibration: 20 Hz

Vertical component of total amplitude: 1.25 to 1.55 mm

                                      TABLE 1                                     __________________________________________________________________________                              Vibrating Conditions                                Specimens                 Vertical                                                                  Dia. of                                                                           Component                                                                           Length of                                                                           Results of Passing                         Outside                                                                            Wall  Inside  Optical                                                                           of Total                                                                            Initial                                                                             Travel                                                                             Passing                               Dia. Thickness                                                                           Dia.                                                                              Length                                                                            Fiber                                                                             Amplitude                                                                           Insertion                                                                           Speed                                                                              Time                               No.                                                                              (mm) (mm)  (mm)                                                                              (m) (mm)                                                                              (mm)  (m)   (m/min.)                                                                           (min.)                             __________________________________________________________________________    1  0.8  0.15  0.5 10,000                                                                            0.4 1.25  150   2    5,000                              2  0.9  0.15  0.6 10,000                                                                            0.4 1.35  120   2.3  4,350                              3  1.0  0.15  0.7 10,000                                                                            0.4 1.45  100   2.6  3,850                              4  1.1  0.15  0.8 10,000                                                                            0.4 1.55  80    3    3,330                              5  1.2  0.15  0.9 10,000                                                                            0.4 1.55  70    3.5  2,860                              6  1.6  0.2   1.2 10,000                                                                            0.4 1.55  60    4    2.500                              7  2.0  0.2   1.6 10,000                                                                            0.4 1.55  30    4    2,500                              __________________________________________________________________________

The obtained results are shown in Table 1.

FIGS. 8a and 8b show the vibrations of the bobbin in Example No. 4 shownin Table 1. While the diagram of FIG. 8a shows a condition in which theoptical fiber is still not inserted in the tube, another diagram of FIG.8b shows a condition in which 1000 m of the optical fiber has beeninserted in the tube. In these diagrams, A_(V) and A_(H) respectivelydesignate the vertical and horizontal components of amplitude. As isobvious from FIG. 8(b), a high-frequency component appeared in thevibration of the coil when the optical fiber has been inserted in thetube. The amplitudes were measured by an accelerometer attached to thebobbin flange.

The test proved that optical fibers can be quite smoothly passed throughthe entire length of steel tubes in the desired periods of time. As isobvious from Table 1, optical fibers can be satisfactorily inserted intotubes having such a small diameter as 2 mm or under and such a largelength as about 10 km. Even in such cases, the optical fibers passedthrough do not deteriorate or get otherwise damaged.

Now other variations of the component parts of the embodiment justdescribed will be described in the following. Similar parts aredesginated by similar reference characters, with the description thereofomitted.

In this invention, a number of circular grooves 67 parallel to theflange 66 of a bobbin 64 may be provided as shown in FIG. 9a. Suchgrooves 67 need not be provided throughout the whole circumference ofthe barrel 65. Instead, grooves 67 and a smooth portion 68 may beprovided in different portions thereof as shown in FIG. 9b.

Smooth passing of an optical fiber through a tube is impracticableunless the tube is kept in close contact with the bobbin because precisetransmission of vibration is not achieved then. The tube readily clingsto the barrel in the direction of the barrel diameter, but not so in thedirection of the barrel axis. This is likely to entail a disturbance invertical vibration.

In FIG. 10, the tube 1 coiled around the barrel of the bobbin 27 iswrapped by a wide elastic belt 71 shown in FIG. 11. The elastic belt 71consists of a flat rubber belt 72 and flanges 73 integrally fastened toboth ends thereof. The tube 1 is tightly pressed in the direction of thediameter of the bobbin 27 by fastening the bolts 75 passed through thebolt holes 74 provided in the opposite flanges 73 with nuts 76 after thecoil of tube 5 has been wrapped by the rubber belt 72. The tighteningforce of the belt 72 can be adjusted by turning the nuts 76.

FIG. 12 shows another means for fastening the coil of tube 5 of thebobbin. A bobbin 79 has a slot 81 and a plurality of stopper grooves 82provided in each flange 80 thereof as shown in FIG. 13. The elastic beltconsists of a rubber belt 84 having stopper rods 85, 86 fastened to bothends thereof. After the tube 1 has been wound around the bobbin 79, thetop and bottom ends of one stopper rod 85 on the belt 84 are inserted inthe slots 81 in the top and bottom flanges. After the belt 84 has beenwound around the tube 1, for example, clockwise in such a manner thatboth ends thereof overlap each other to some extent, the belt 84 isfastened by inserting the top and bottom ends of the other stopper rod86 in an appropriate stopper groove 82. The elastic belt 84 thus keepsthe tube 1 in close contact with the barrel 83 of the bobbin 27, withthe tightening force thereof being adjusted by choosing a stopper groove82 in an appropriate position.

FIG. 15 shows still another means for fastening the coil of tube to thebobbin 27. After the tube 1 has been wound around the barrel of thebobbin 27 (in a single or more rings), the tube 1 is fastened inposition by an adhesive tape 88 that is wrapped therearound asillustrated. To ensure secure fastening, the adhesive tape 88 is wrappedin a partially or fully overlapped manner. Any kind of adhesive tapeserves the purpose so long as it has enough adhesive force to tightlypress the tube 1 wound around the barrel of the bobbin 27 thereagainstand keep the tube 1 in such tightly pressed condition for a certainperiod of time. But the adhesive tape 88 should preferably be of suchtype as can be easily peeled off by hand when the tube 1 is detachedfrom the bobbin 27 after the optical fiber 7 has been passedtherethrough. For example, gummed tape is one of the most suitableadhesive tapes of such kind.

Any of the above-described fastening means keeps the tube 1 in closecontact with the barrel of the bobbins 27, 79, thereby ensuring precisetransmission of the vibration of the bobbin 27, 79 to the tube 1 whilekeeping to a minimum the freedom and wild vibration of the tube 1. Withthe undesirable motion of the tube in the direction of the bobbin axisand diameter thus effectively held down, the optical fiber can besmoothly and efficiently passed through the coil of tube. There is yetanother embodiment in which the tube is wound around a bobbin that iscircularly divided into two or more segments. Then, the bobbin isexpanded outward from inside, using a hydraulic jack, link mechanism orthe like, thereby bringing the coil of tube into close contact with thebobbin.

FIG. 16 shows another embodiment of the anti-vibrating guide. The guidecylinder proper 91 of an anti-vibrating guide 90 has a heavier wallthickness. The guide ends 92 are rounded off to leave no angular cornersthereat. The anti-vibrating guide is of course not limited to theillustrated embodiments, but may be of any shape and structure so longas no damage is caused to the optical fiber at the inlet end 2 of thetube.

FIG. 17 shows another embodiment of the protective guide. Instead ofattaching a separate protective guide, the inlet end 2 of the tubeitself may be expanded to form a larger-diameter portion 94 as shown inFIG. 17. This embodiment will also produce similar results.

A pair of rollers covered with sponge or other cushioning material or apiece of cushioning material that may hold the optical fiber in suchmanner as not to impede the smooth travel thereof may be provided nearthe inlet end of the tube as the protective guide.

The number of optical fiber to be passed through a tube is not limitedto one. A plurality of optical fibers may be passed through if therelationship between the inside diameter of the tube and the diameter ofthe optical fiber 7 allows.

This invention is of course not limited to a combination of the opticalfiber consisting of a precoated element fiber and the steel tube used inthe embodiments described hereinbefore. Many other variations arepossible, such as those in which an optical fiber or cable is passedthrough tubes if aluminum, synthetic resin or other materials. Theoptical fiber passed through the tube may be subjected to a processingthat reduces the cross-sectional area thereof. Other appropriatemodifications may be introduced as required. The optical fiber may befed from the top of the coil of tube. The central axis of the coil oftube should preferably agree with the central axis of the helix, thoughsuch agreement is not an absolute requisite. The central axis of thecoil of tube should preferably be vertical, but need not always be so.For initial insertion of the optical fiber, pinch rollers or othermechanical means may be used instead of manual insertion.

What is claimed is:
 1. A method of passing an optical fiber through atube which comprises the steps of:forming a coil of the tube; causingthe coil of the tube to vibrate in such a manner that a given pointthereof reciprocates along a helical path; feeding the optical fiberinto one end of the coil of tube that is being thus vibrated, whereuponthe optical fiber fed into the tube moves forward under the influence ofthe intermittent conveying force exerted by the inner wall of the tubein the direction of the circumference of the coil of tube, said feedingstep including positively feeding the optical fiber into the coil oftube at substantially the same speed as the speed of forward movement ofthe optical fiber through the coil of tube.
 2. The method according toclaim 1, in which the optical fiber is previously inserted into the tubefrom one end thereof in such a length that a conveying force greatenough to pull in the optical fiber is developed.
 3. The methodaccording to claim 1, in which the optical fiber is fed into the tube insuch a manner that the upstream-oriented force working on the opticalfiber at the inlet of the tube is kept smaller than said conveyingforce.
 4. The method according to claim 1, in which a lubricant iscoated on the surface of the optical fiber that is to be passed into thetube.
 5. The method of passing an optical fiber through a tube accordingto claim 1, in which the optical fiber is fed into one end of the coilof tube by slackening the optical fiber upstream of said end so that acounterforce exerted at said end on the optical fiber is not larger thansaid conveying force.
 6. A method of passing an optical fiber through atube which comprises the steps of:forming a coil of the tube; causingthe coil of tube to vibrate in such a manner that a given point thereofreciprocates along a helical path; feeding the optical fiber into oneend of the coil of tube that is being thus vibrated, whereupon theoptical fiber fed into the tube moves forward under the influence of theintermittent conveying force exerted by the inner wall of the tube inthe direction of the circumference of the coil of tube; detecting anydifferent between the speed of movement of the optical fiber through thetube and the feeding speed of the optical fiber; and controlling thefeeding speed of the optical fiber on the basis of the speed differencethus detected.
 7. The method of passing an optical fiber through a tubeaccording to claim 6, in which said speed difference is detected fromslack in the optical fiber.
 8. A method of passing an optical fiberthrough a tube which comprises the steps of:forming a coil of the tube;causing the coil of tube to vibrate in such a manner that a given pointthereof reciprocates along a helical path; and feeding the optical fiberinto one end of the coil of tube that is being thus vibrated whilekeeping the optical fiber from vibrating upstream of the entry end ofthe tube, whereupon the optical fiber fed into the tube moves forwardunder the influence of the intermittent conveying force exerted by theinner wall of the tube in the direction of the circumference of the coiltube.